Examining the Influence of Cognitive Load and Environmental Conditions on Autonomic Nervous System Response in Military Aircrew: A Hypoxia-Normoxia Study.

Executing flight operations demand that military personnel continuously perform tasks that utilize low- and high-order cognitive functions. The autonomic nervous system (ANS) is crucial for regulating the supply of oxygen (O2) to the brain, but it is unclear how sustained cognitive loads of different complexities may affect this regulation. Therefore, in the current study, ANS responses to low and high cognitive loads in hypoxic and normoxic conditions were evaluated. The present analysis used data from a previously conducted, two-factor experimental design. Healthy subjects (n = 24) aged 19 to 45 years and located near Fort Novosel, AL, participated in the parent study. Over two, 2-h trials, subjects were exposed to hypoxic (14.0% O2) and normoxic (21.0% O2) air while simultaneously performing one, 15-min and one, 10-min simulation incorporating low- and high-cognitive aviation-related tasks, respectively. The tests were alternated across five, 27-min epochs; however, only epochs 2 through 4 were used in the analyses. Heart rate (HR), HR variability (HRV), and arterial O2 saturation were continuously measured using the Warfighter MonitorTM (Tiger Tech Solutions, Inc., Miami, FL, USA), a previously validated armband device equipped with electrocardiographic and pulse oximetry capabilities. Analysis of variance (ANOVA) regression models were performed to compare ANS responses between the low- and high-cognitive-load assessments under hypoxic and normoxic conditions. Pairwise comparisons corrected for familywise error were performed using Tukey's test within and between high and low cognitive loads under each environmental condition. Across epochs 2 through 4, in both the hypoxic condition and the normoxic condition, the high-cognitive-load assessment (MATB-II) elicited heightened ANS activity, reflected by increased HR (+2.4 ± 6.9 bpm) and decreased HRV (-rMSSD: -0.4 ± 2.7 ms and SDNN: -13.6 ± 14.6 ms). Conversely, low cognitive load (ADVT) induced an improvement in ANS activity, with reduced HR (-2.6 ± 6.3 bpm) and increased HRV (rMSSD: +1.8 ± 6.0 ms and SDNN: vs. +0.7 ± 6.3 ms). Similar observations were found for the normoxic condition, albeit to a lower degree. These within-group ANS responses were significantly different between high and low cognitive loads (HR: +5.0 bpm, 95% CI: 2.1, 7.9, p < 0.0001; rMSSD: -2.2 ms, 95% CI: -4.2, -0.2, p = 0.03; SDNN: -14.3 ms, 95% CI: -18.4, -10.1, p < 0.0001) under the hypoxic condition. For normoxia, significant differences in ANS response were only observed for HR (+4.3 bpm, 95% CI: 1.2, 7.4, p = 0.002). Lastly, only high cognitive loads elicited significant differences between hypoxic and normoxic conditions but just for SDNN (-13.3 ms, 95% CI, -17.5, -8.9, p < 0.0001). Our study observations suggest that compared to low cognitive loads, performing high-cognitive-load tasks significantly alters ANS activity, especially under hypoxic conditions. Accounting for this response is critical, as military personnel during flight operations sustain exposure to high cognitive loads of unpredictable duration and frequency. Additionally, this is likely compounded by the increased ANS activity consequent to pre-flight activities and anticipation of combat-related outcomes.

Continuous Physiological Monitoring of the Combined Exposure to Hypoxia and High Cognitive Load in Military Personnel.

Military aviators endure high cognitive loads and hypoxic environments during flight operations, impacting the autonomic nervous system (ANS). The synergistic effects of these exposures on the ANS, however, are less clear. This study investigated the simultaneous effects of mild hypoxia and high cognitive load on the ANS in military personnel. This study employed a two-factor experimental design. Twenty-four healthy participants aged between 19 and 45 years were exposed to mild hypoxia (14.0% O2), normoxia (21.0% O2), and hyperoxia (33.0% O2). During each epoch (n = 5), participants continuously performed one 15 min and one 10 min series of simulated, in-flight tasks separated by 1 min of rest. Exposure sequences (hypoxia-normoxia and normoxia-hyperoxia) were separated by a 60 min break. Heart rate (HR), heart rate variability (HRV), and O2 saturation (SpO2) were continuously measured via an armband monitor (Warfighter MonitorTM, Tiger Tech Solutions, Inc., Miami, FL, USA). Paired and independent t-tests were used to evaluate differences in HR, HRV, and SpO2 within and between exposure sequences. Survival analyses were performed to assess the timing and magnitude of the ANS responses. Sympathetic nervous system (SNS) activity during hypoxia was highest in epoch 1 (HR: +6.9 bpm, p = 0.002; rMSSD: -9.7 ms, p = 0.003; SDNN: -11.3 ms, p = 0.003; SpO2: -8.4%, p < 0.0000) and appeared to slightly decline with non-significant increases in HRV. During normoxia, SNS activity was heightened, albeit non-significantly, in epoch 1, with higher HR (68.5 bpm vs. 73.0 bpm, p = 0.06), lower HRV (rMSSD: 45.1 ms vs. 38.7 ms, p = 0.09 and SDNN: 52.5 ms vs. 45.1 ms, p = 0.08), and lower SpO2 (-0.7% p = 0.05). In epochs 2-4, HR, HRV, and SpO2 trended towards baseline values. Significant between-group differences in HR, HRV, and O2 saturation were observed. Hypoxia elicited significantly greater HRs (+5.0, p = 0.03), lower rMSSD (-7.1, p = 0.03), lower SDNN (-8.2, p = 0.03), and lower SpO2 (-1.4%, p = 0.002) compared to normoxia. Hyperoxia appeared to augment the parasympathetic reactivation reflected by significantly lower HR, in addition to higher HRV and O2 relative to normoxia. Hypoxia induced a greater ANS response in military personnel during the simultaneous exposure to high cognitive load. The significant and differential ANS responses to varying O2 levels and high cognitive load observed highlight the importance of continuously monitoring multiple physiological parameters during flight operations.

Evaluation of the Commercial, Off-the-Shelf (COTS) King-Devick Eye Tracking System.

Concussion biomarkers are important guides for diagnosis and return-to-duty decisions. Recent literature describes the King-Devick (KD) test as a sensitive sports-related concussion screener. This test involves timing an individual reading aloud 120 digits printed on three test cards. The test is commonly considered to evaluate the effects of concussion and other factors on reading-related eye movements (EMs). However, the extent to which the KD test reflects EMs remains a matter of conjecture since the test reports only reading speed and number of errors. An off-the-shelf, computerized KD with eye tracking system recently became commercially available. Two early model KD with eye tracking systems were purchased in 2015 and evaluated before deploying them for research. The evaluation consisted of two studies; one with 20 volunteers assessing the comparability of the two systems and the other with 5 volunteers to quantify the systems' stability and repeatability over 5 successive days. The results showed that several of the systems' reported EM response parameters lacked face validity; consequently, the systems could not be used for scientific research. This conclusion emphasizes the importance of systematic test and evaluation of new equipment before it is used for research.

A Novel, Inexpensive Method to Monitor, Record, and Analyze Breathing Behavior During Normobaric Hypoxia Generated by the Reduced Oxygen Breathing Device.

OBJECTIVES: Since hypoxia remains one of the most important physiological hazards the aviation environment poses, military aviators are trained to recognize symptoms of hypoxia in order to implement appropriate safety procedures and countermeasures when hypoxia occurs. A widely used commercial instrument for hypoxia training, demonstration, and research is the Reduced Oxygen Breathing Device (ROBD). Here we describe a novel, inexpensive method to use the ROBD's breathing loop pressure (BLP) to measure respiration rate, a critically important response parameter for hypoxia. METHODS: The ROBD can be controlled by a computer to export several variables including BLP, via the ROBD's RS232 port. An archived database was reanalyzed to assess the BLP data. New instrumentation added independent measures of respiration and expired oxygen and carbon dioxide; these measures were integrated with the ROBD output. RESULTS: Analysis of the archived data showed that the BLP reflected realistic breathing patterns. The new instrumentation integrated well with the ROBD, and independently supported the potential of the BLP as a valid measure of respiration. DISCUSSION: The ROBD's BLP data may provide a basis for a reliable, sensitive measure of respiration that is available at no additional cost.

Visual Dysfunctions at Different Stages after Blast and Non-blast Mild Traumatic Brain Injury.

PURPOSE: To assess the prevalence of visual dysfunctions and associated symptoms in war fighters at different stages after non-blast- or blast-induced mild traumatic brain injury (mTBI). METHODS: A comprehensive retrospective review of the electronic health records of 500 U.S. military personnel with a diagnosis of deployment-related mTBI who received eye care at the Landstuhl Regional Medical Center. For analysis, the data were grouped by mechanism of injury, and each group was further divided in three subgroups based on the number of days between injury and initial eye examination. RESULTS: The data showed a high frequency of visual symptoms and visual dysfunctions. However, the prevalence of visual symptoms and visual dysfunctions did not differ significantly between mechanism of injury and postinjury stage, except for eye pain and diplopia. Among visual symptoms, binocular dysfunctions were more common, including higher near vertical phoria, reduced negative fusional vergence break at near, receded near point of convergence, decreased stereoacuity, and reduced positive relative accommodation. CONCLUSIONS: The lack of difference in terms of visual sequelae between subgroups (blast vs. nonblast) suggests that research addressing the assessment and management of mTBI visual sequelae resulting from civilian nonblast events is relevant to military personnel where combat injury results primarily from a blast event.

Feasibility of using normobaric hypoxic stress in mTBI research.

Studies of mild traumatic brain injury (mTBI) recovery generally assess patients in unstressed conditions that permit compensation for impairments through increased effort expenditure. This possibility may explain why a subgroup of individuals report persistent mTBI symptoms yet perform normally on objective assessment. Accordingly, the development and utilization of stress paradigms may be effective for enhancing the sensitivity of mTBI assessment. Previous studies, discussed here, indirectly but plausibly support the use of normobaric hypoxia as a stressor in uncovering latent mTBI symptoms due to the overlapping symptomatology induced by both normobaric hypoxia and mTBI. Limited studies by our group and others further support this plausibility through proof-of-concept demonstrations that hypoxia reversibly induces disproportionately severe impairments of oculomotor, pupillometric, cognitive and autonomic function in mTBI individuals.

A History of Mild Traumatic Brain Injury Affects Peripheral Pulse Oximetry during Normobaric Hypoxia.

INTRODUCTION: Physiological and emotional stressors increase symptoms of concussion in recently injured individuals and both forms of stress-induced symptoms in people recovering from mild traumatic brain injury (mTBI), but who are asymptomatic when not stressed or are at rest. METHODS: Healthy asymptomatic adults (25.0 ± 5.1 years) with a history of mTBI (n = 36) and matched healthy controls (HC) (n = 36) with no mTBI history were exposed to three levels of normobaric hypoxic stress generated with the Reduced Oxygen Breathing Device (ROBD) (Environics, Inc., Tollande, CT, USA), which reduced the percent O2 by mixing sea level air with nitrogen. The ROBD reduced the percent O2 in the breathable air from the normal 21% to 15.5% O2, 14% O2, and 13% O2. Under these conditions: (a) a standard pulse oximeter recorded peripheral oxygen saturation (SpO2) and pulse rate (beats per minute) and (b) the Functional Impairment Tester (FIT) (PMI, Inc., Rockville, MD, USA) recorded saccadic velocity and pupillary response dynamics to a brief light flash. RESULTS: For all three hypoxic stress conditions, the mTBI group had significantly higher SpO2 during the final minute of exposure than did the controls [F(2.17,151.8) = 5.29, p < 0.001, η2 = 0.852] and the rate of SpO2 change over time was significantly shallower for the mTBI than for the controls [F(2.3,161.3) = 2.863, p < 0.001, η2 = 0.569], Greenhouse-Geisser corrected. Overall, mTBI had lower pulse rate but the difference was only significant for the 14% O2 condition. FIT oculomotor measures were not sensitive to group differences. When exposed to mild or moderate normobaric hypoxic stress (15% O2): (1) SpO2 differences emerged between the mTBI and matched HC groups, (2) heart rate trended lower in the mTBI group, and (3) FIT measures were not sensitive to group differences. CONCLUSION: A relatively minor hypoxic challenge can reveal measurable differences in SpO2 and heart rate in otherwise asymptomatic individuals with a history of mTBI.

A Performance Comparison of Color Vision Tests for Military Screening.

BACKGROUND: Current color vision (CV) tests used for aviation screening in the U.S. Army only provide pass-fail results, and previous studies have shown variable sensitivity and specificity. The purpose of this study was to evaluate seven CV tests to determine an optimal CV test screener that potentially could be implemented by the U.S. Army. METHODS: There were 133 subjects [65 Color Vision Deficits (CVD), 68 Color Vision Normal (CVN)] who performed all of the tests in one setting. CVD and CVN determination was initially assessed with the Oculus anomaloscope. Each test was administered monocularly and according to the test protocol. The main outcome measures were test sensitivity, specificity, and administration time (automated tests). RESULTS: Three of the four Pseudoisochromatic Plate (PIP) tests had a sensitivity/specificity > 0.90 OD/OS, whereas the FALANT tests had a sensitivity/specificity > 0.80 OD/OS. The Cone Contrast Test (CCT) demonstrated sensitivity/specificity > 0.90 OD/OS, whereas the Color Assessment and Diagnosis (CAD) test demonstrated sensitivity/specificity > 0.85 OD/OS. Comparison with the anomaloscope ("gold standard") revealed no significant difference of sensitivity and specificity OD/OS with the CCT, Dvorine PIP, and PIPC tests. Finally, the CCT administration time was significantly faster than the CAD test. DISCUSSION: The current U.S. Army CV screening tests demonstrated good sensitivity and specificity, as did the automated tests. In addition, some current PIP tests (Dvorine, PIPC), and the CCT performed no worse statistically than the anomaloscope with regard to sensitivity/specificity. The CCT letter presentation is randomized and results would not be confounded by potential memorization, or fading, of book plates.

Effects of repetitive low-level blast exposure on visual system and ocular structures.

UNLABELLED: The purpose of this study was to determine whether repetitive exposure to low-level blasts during military breacher training produces acute and cumulative damage to the ocular tissues or visual system. The effects of low-level blast exposure on high-contrast visual acuity, contrast sensitivity, oculomotor function, color vision, visual field (VF), pupillary light reflex, corneal endothelial cell density (ECD), macular thickness, retinal nerve fiber layer thickness, and cup-to-disc ratio were assessed using a battery of standard clinical ophthalmic tests administered 10 times over a 2-year period. Data from nine breacher instructors (Cadre) were compared with data from four breacher engineers (CONTROL). The Cadre group showed higher vertical deviation at near than the CONTROL group over time. The VF mean deviation on the left eye that tended to be worse in the Cadre group was worse throughout the study, suggesting a decrease in VF sensitivity (Cadre: -0.20 +/- 0.15 dB; CONTROL: 1.05 +/- 0.15 dB; p = 0.03). The Cadre group had a reduced ECD (right eye: Cadre 2,502 cells/mm(2) vs CONTROL 2,808 cells/mm(2), p = 0.05; left eye: Cadre 2,558 cells/mm(2) vs CONTROL 2,892 cells/mm(2), p = 0.04). These results suggest that even low-level primary blast has the potential to produce occult eye injury.

Visual field dysfunctions in warfighters during different stages following blast and nonblast mTBI.

OBJECTIVES: Traumatic brain injury (TBI) is the leading injury coming out of the past decades' two major military conflicts, with mild TBI (mTBI) being the most commonly diagnosed form. The aim of this study was to assess the frequency and types of visual field (VF) defects seen at different testing stages following nonblast and blast-induced mTBI. METHODS: A comprehensive retrospective review was performed on 500 electronic health records for military personnel sustaining an mTBI during deployment, of which 166 patients were tested with both confrontation VF and 30-2 Humphrey Matrix Frequency Doubling Technology (FDT) perimetry. RESULTS: Scatter defects (48%) were the most predominantly found deficits in both blast and nonblast mTBI injury mechanisms and over postinjury test time frames. Confrontation VF was shown to be a poor qualitative predictor of VF defect. A profound decrease in VF sensitivity was noted in comparison to previously reported FDT normative data. Finally, a significant trend of decreasing VF defects was seen over time, indicating the potential usage of FDT as a visual biomarker for monitoring mTBI recovery. CONCLUSIONS: The findings of this study highlight the importance of performing threshold perimeter testing in those who have suffered an mTBI or concussion-like event.

Uncovering latent deficits due to mild traumatic brain injury by using normobaric hypoxia stress.

Memory deficits and other cognitive symptoms frequently associated with mTBI are commonly thought to resolve within 7-10 days. This generalization is based principally on observations made in individuals who are in the unstressed environmental conditions typical of a clinic and so does not consider the impact of physiologic, environmental, or psychological stress. Normobaric hypoxic stress can be generated with normal mean sea level (MSL) air, which is about 21% oxygen (O2) and 78% nitrogen (N), by reducing the percentage of O2 and increasing the percentage of N so that the resultant mixed-gas has a partial pressure of O2 approximating that of specified altitudes. This technique was used to generate normobaric hypoxic equivalents of 8,000, 12,000, and 14,000 feet above MSL in a group of 36 volunteers with a mTBI history and an equal number of controls matched on the basis of age, gender, tobacco smoking consumption, weight, height, and body mass index. Short-term visual memory was tested using the Matching to Sample (M2S) subtest of the BrainCheckers analog of the Automated Neuropsychological Assessment Metrics. Although there were no significant differences in M2S performance between the two groups of subjects at MSL, with increased altitude, the mTBI group performance was significantly worse than that of the control group. When the subjects were returned to MSL, the difference disappeared. This finding suggests that the "hypoxic challenge" paradigm developed here has potential clinical utility for assessing the effects of mTBI in individuals who appear asymptomatic under normal conditions.

An independent, objective calibration check for the reduced oxygen breathing device.

INTRODUCTION: Normobaric hypoxia, which does not entail an altitude chamber, but reduces the fraction of inspired oxygen (02) by diluting air with nitrogen, is finding increased use. The reduced oxygen breathing device (ROBD-2) is one of several commercial devices for generating such normobaric hypoxia. Reported here are results of a procedure to check the calibration of the ROBD-2 using methods that may be readily available in physiology and psychophysiology facilities. METHODS: The %O2 output by the ROBD-2 was measured concurrently in two ways for altitudes from mean sea level (MSL) to 34,000 ft above MSL at 2000-ft intervals five times over 2 d. One measurement method used was the one built into the ROBD-2, which reports the %O2 the device is delivering at the selected target altitude. The other method diverted a sample of the ROBD-2's output gas to the paramagnetic O2, sensor of a metabolic measuring system via its sampling line. The %O2, measured with the two techniques was compared using Bland-Altman statistical procedures. RESULTS: The two measurement methods produced %O2 readings differing by no more than 0.18% O2 from MSL to 34,000 ft (from 20.95 to about 4.40% oxygen, respectively), the full operating range of the device. Calculating altitude from the measured %O2 showed the ROBD-2 operated within its design error margins over its whole operational range. DISCUSSION: The purpose for which the ROBD-2 is used should determine whether the reliability of its output in normobaric equivalent altitude is adequate. Differences between devices and device stability over time and with use have yet to be assessed. Our assessment does not address the accuracy of the algorithm the ROBD-2 uses to provide an equivalent target altitude under normobaric conditions.

Visual dysfunctions and symptoms during the subacute stage of blast-induced mild traumatic brain injury.

The purpose of the present study was to assess the occurrence of visual dysfunctions and associated symptoms in active duty warfighters during the subacute stage of blast-induced mild traumatic brain injury (mTBI). A comprehensive visual and oculomotor function evaluation was performed on 40 U.S. military personnel, 20 with blast-induced mTBI and 20 without. In addition, a comprehensive symptom questionnaire was used to assess the frequency of visual, vestibular, and neuropsychiatric-associated symptoms. The most common mTBI-induced visual dysfunctions were associated with near oculomotor deficits, particularly large exophoria, decreased fusion ranges, receded near point of convergence, defective pursuit and saccadic eye movements, decreased amplitude of accommodation, and monocular accommodative facility. These were associated with reduced reading speed and comprehension and an increased Convergence Insufficiency Symptom Survey score. Photosensitivity was a common visual dysfunction along with hearing, balance, and neuropsychiatric symptoms. The oculomotor testing for warfighters suspected of blast-induced mTBI should include, at a minimum, the assessment of near lateral and vertical phorias, positive fusional vergence, stereoacuity, near point of convergence, amplitude of accommodation, monocular accommodative facility, saccades, and pursuit eye movements. A reading test should be included in all routine exams as a functional assessment of the integration of oculomotor functions.

Effectiveness of computerized oculomotor vision screening in a military population: pilot study.

The prevalence of oculomotor dysfunctions associated with blast-induced mild traumatic brain injury (mTBI) in warfighters has increased as a consequence of recent conflicts. This study evaluated the effectiveness of computerized oculomotor vision screening (COVS) in a military population. Oculomotor functions were assessed with COVS and by conventional methods in 20 U.S. military personnel with and 20 without mTBI. The validity of COVS was determined by Pearson correlation and Bland-Altman method or the kappa coefficient. The repeatability of the COVS was assessed with the coefficient of repeatability or the kappa coefficient. The results showed that COVS had high sensitivity and specificity for screening near oculomotor functions. Overall, the COVS showed excellent validity and repeatability for assessing near lateral and vertical phorias, Worth 4 Dot, and fixation, as well as pursuit and saccadic eye movements. Despite the strong Pearson correlation, the Bland-Altman analysis identified minor to moderate discrepancies for both positive and negative fusional vergence and their associated recovery as well as for the monocular accommodative facility measurements. This study demonstrated that non-eye-care professionals may be able to use the COVS as a tool to efficiently screen oculomotor functions in a military population with or without mTBI.

Hypoxia and flight performance of military instructor pilots in a flight simulator.

INTRODUCTION: Military aircrew and other operational personnel frequently perform their duties at altitudes posing a significant hypoxia risk, often with limited access to supplemental oxygen. Despite the significant risk hypoxia poses, there are few studies relating it to primary flight performance, which is the purpose of the present study. METHODS: Objective, quantitative measures of aircraft control were collected from 14 experienced, active duty instructor pilot volunteers as they breathed an air/nitrogen mix that provided an oxygen partial pressure equivalent to the atmosphere at 18,000 ft (5486.4 m) above mean sea level. The flight task required holding a constant airspeed, altitude, and heading at an airspeed significantly slower than the aircraft's minimum drag speed. The simulated aircraft's inherent instability at the target speed challenged the pilot to maintain constant control of the aircraft in order to minimize deviations from the assigned flight parameters. RESULTS: Each pilot's flight performance was evaluated by measuring all deviations from assigned target values. Hypoxia degraded the pilot's precision of altitude and airspeed control by 53%, a statistically significant decrease in flight performance. The effect on heading control effects was not statistically significant. There was no evidence of performance differences when breathing room air pre- and post-hypoxia. DISCUSSION: Moderate levels of hypoxia degraded the ability of military instructor pilots to perform a precision slow flight task. This is one of a small number of studies to quantify an effect of hypoxia on primary flight performance.

Head position of helicopter pilots during slalom maneuvers.

INTRODUCTION: Pilots typically tilt their heads when executing coordinated banking turns, a phenomenon commonly attributed to the putative opto-kinetic cervical reflex (OKCR). The OKCR is usually described as a reflex, primarily driven by stimuli in the visual periphery, and is important to a pilot's spatial orientation by providing a relatively stabilized horizontal frame of reference. The present paper presents an alternative hypothesis for the observed head tilting seen in pilots. METHODS: An archived data set, originally collected for other purposes, contained the head turn, pitch, and tilt of 4 helicopter pilots recorded at 10 Hz as the pilots executed 42 slalom maneuvers in an AH Mk 7 Lynx helicopter under visual flight conditions. The analytic method was a correlational analysis of head turn, pitch, and tilt. RESULTS: As expected, pilots routinely tilted their heads during the slaloms in a fashion typically attributed to the OKCR. Correlations among head turn, tilt, and pitch showed that when the helicopter turned left, the head, presumably to look into the turn, turned left and also pitched up and tilted right. Similarly, when the helicopter turned right, the head, presumably to look into the turn, turned right, pitched up, and tilted left. CONCLUSIONS: The head tilting usually attributed to a neuromuscular reflex driven by visual stimuli may be a biomechanical consequence of the head posture pilots assume when they simply look where they are going, eliminating the need to postulate the existence of a novel neuromuscular reflex.

Ethics in human experimentation: the two military physicians who helped develop the Nuremberg Code.

The Nuremberg Code is generally considered the beginning of modern ethics in human experimentation. The Code is a list of 10 principles that Judge Walter Beals included in the judgment he delivered at the close of the Nuremberg Medical Trial on 19 August 1947. Recently, scholars have studied the origin of the Code, who wrote it, and why. This is important to military medicine and the Aerospace Medical Association in particular because many of the defendants claimed their crimes were experiments in aviation and environmental physiology conducted under wartime conditions. The chief prosecutor of the Nuremberg Medical Trial, General Telford Taylor, relied on the guidance of an advisor provided by the American Medical Association, Andrew C. Ivy, one of the foremost physiologists of his time. The neurologist, Leo Alexander, then a colonel in the U.S. Army Reserves, was another medical advisor. Both men were crucial to the development of Taylor's courtroom strategy. The material Alexander and Ivy provided was incorporated verbatim in the section of the judgment that became the Code. Although both men contributed to the Code, Ivy provided what seems to be the first formulation of many of these principles during a meeting of Allied medical investigators at the Pasteur Institute in July 1946. Naval researchers should note that Ivy had been the Director of the Research Division of the Naval Medical Research Institute when it was commissioned on October 27, 1942.

The economic context for the development of "blind flight".

On 24 September 1929, at Mitchel Field, Long Island, NY, Jimmy Doolittle performed the first so-called "blind flight." He executed a flight plan and landed using only cockpit instruments, a feat that culminated a research program supported by the Daniel Guggenheim Fund for the Promotion of Aeronautics. Contemporary aviation medicine, with its understanding of the challenges of spatial (dis)orientation, has a special understanding and appreciation of the complex human performance, medical and technical problems that had to be overcome to make instrument flight possible. It is likely that the problems would not have been solved unless a socioeconomic context provoked a sufficient motivation to address them. This paper outlines some of the economic factors that motivated the research and development necessary for instrument flight. These factors were the direct consequence of the sudden, huge explosion of the aviation industry caused by World War I, and with the Armistice, the equally sudden loss of the industry's primary customer, the military. Finding a civilian role for aviation awaited the development of air mail, which, in turn, depended on the ability to fly according to a reliable schedule. The need to reliably adhere to a schedule forced the scientific and technological research needed to develop all-weather, blind flight.

Civilian use of night vision goggles.

Civil aviation operators have expressed an increased interest in conducting night operations with night vision imaging systems. The development of special operational concepts, hardware requirements, training requirements, and regulatory change and oversight is necessary to control for the known performance constraints associated with these devices. In 2001, the Aerospace Medical Association initiated an internal request to review the human factors issues concerning the use of night vision goggles (NVGs) in civilian flight operations. This paper provides some basic information on night vision imaging systems to highlight the Association's position for supporting the appropriate use of NVGs in civilian aviation while concurrently expressing the need for a judicious and studied approach to their deployment.